R help - Apr 2010 - how to remove one row at a time from a matrix keeping its nrow consistent

After some headache with debugging my script, I finally isolated the problem
taht I am going to illustrate in the following example.
I expected matrix nrow to decrease consistently till 1. Instead, when the matrix
is left with one row only, its nrow jumps to 2 because the matrix
gets transposed. How come ?
Thank you,
Maura 
> B <- c(1,2)
>  B <- rbind(B,c(3,4))
>  B <- rbind(B,c(5,6))
>  B
  [,1] [,2]
B    1    2
     3    4
     5    6
> dim(B)
[1] 3 2
> nrow(B)
[1] 3
> 
> #REMOVE ROW-1 OUT OF 3 
>  B <- as.matrix(B[-1,])
>  B
 [,1] [,2]
    3    4
    5    6
> dim(B)
[1] 2 2
> nrow(B)
[1] 2
> 
> #REMOVE ROW-2 OUT OF 3
>  B <- as.matrix(B[-1,])
>  B
     [,1]
[1,]    5
[2,]    6
> dim(B)
[1] 2 1
> nrow(B)
[1] 2



tutti i telefonini TIM!


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On Sat, Apr 17, 2010 at 7:25 PM,  <mauede at alice.it>
wrote:
> After some headache with debugging my script, I finally isolated the
problem taht I am going to illustrate in the following example.
> I expected matrix nrow to decrease consistently till 1. Instead, when the
matrix is left with one row only, its nrow jumps to 2 because the matrix
> gets transposed. How come ?
Because the one-row matrix gets reduced to a vector:
> B <- matrix(1:4, nrow = 2, byrow = TRUE)
> class(B)
[1] "matrix"
> B1 <- B[-1,]
> class(B1)
[1] "integer"

and as.matrix applied to a vector produces a one-column matrix (see ?as.matrix).
> Thank you,
> Maura
>
>> B <- c(1,2)
>> ?B <- rbind(B,c(3,4))
>> ?B <- rbind(B,c(5,6))
>> ?B
> ?[,1] [,2]
> B ? ?1 ? ?2
> ? ? 3 ? ?4
> ? ? 5 ? ?6
>> dim(B)
> [1] 3 2
>> nrow(B)
> [1] 3
>>
>> #REMOVE ROW-1 OUT OF 3
>> ?B <- as.matrix(B[-1,])
>> ?B
> ?[,1] [,2]
> ? ?3 ? ?4
> ? ?5 ? ?6
>> dim(B)
> [1] 2 2
>> nrow(B)
> [1] 2
>>
>> #REMOVE ROW-2 OUT OF 3
>> ?B <- as.matrix(B[-1,])
>> ?B
> ? ? [,1]
> [1,] ? ?5
> [2,] ? ?6
>> dim(B)
> [1] 2 1
>> nrow(B)
> [1] 2
>
>
>
> tutti i telefonini TIM!
>
>
> ? ? ? ?[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org

Try this indeed of as.matrix(...) :

B <- B[-1,, drop = FALSE]


On Sat, Apr 17, 2010 at 3:25 PM,  <mauede@alice.it>
wrote:
> After some headache with debugging my script, I finally isolated the
problem taht I am going to illustrate in the following
example.
> I expected matrix nrow to decrease consistently till 1. Instead, when the
matrix is left with one row only, its nrow jumps to 2 because the
matrix
> gets transposed. How come ?
> Thank you,
> Maura
>
>> B <- c(1,2)
>>  B <- rbind(B,c(3,4))
>>  B <- rbind(B,c(5,6))
>>  B
>  [,1] [,2]
> B    1    2
>     3    4
>     5    6
>> dim(B)
> [1] 3 2
>> nrow(B)
> [1] 3
>>
>> #REMOVE ROW-1 OUT OF 3
>>  B <- as.matrix(B[-1,])
>>  B
>  [,1] [,2]
>    3    4
>    5    6
>> dim(B)
> [1] 2 2
>> nrow(B)
> [1] 2
>>
>> #REMOVE ROW-2 OUT OF 3
>>  B <- as.matrix(B[-1,])
>>  B
>     [,1]
> [1,]    5
> [2,]    6
>> dim(B)
> [1] 2 1
>> nrow(B)
> [1] 2
>
>
>
> tutti i telefonini TIM!
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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On Apr 17, 2010, at 2:25 PM, <mauede at alice.it> wrote:
> After some headache with debugging my script, I finally isolated the  
> problem taht I am going to illustrate in the following example.
> I expected matrix nrow to decrease consistently till 1. Instead,  
> when the matrix is left with one row only, its nrow jumps to 2  
> because the matrix
> gets transposed. How come ?
Because you did not use drop=FALSE? (And I think it's a FAQ.)

 > #REMOVE ROW-1 OUT OF 3
 > B <- as.matrix(B[-1,,drop=FALSE])
 > B
  [,1] [,2]
     3    4
     5    6
 > #REMOVE ROW-2 OUT OF 3
 > B <- as.matrix(B[-1, ,drop=FALSE])
 > B
  [,1] [,2]
     5    6

 > nrow(B)
[1] 1

> Thank you,
> Maura
>
>> B <- c(1,2)
>> B <- rbind(B,c(3,4))
>> B <- rbind(B,c(5,6))
>> B
>  [,1] [,2]
> B    1    2
>     3    4
>     5    6
>> dim(B)
> [1] 3 2
>> nrow(B)
> [1] 3
>>
>> #REMOVE ROW-1 OUT OF 3
>> B <- as.matrix(B[-1,])
>> B
> [,1] [,2]
>    3    4
>    5    6
>> dim(B)
> [1] 2 2
>> nrow(B)
> [1] 2
>>
>> #REMOVE ROW-2 OUT OF 3
>> B <- as.matrix(B[-1,])
>> B
>     [,1]
> [1,]    5
> [2,]    6
>> dim(B)
> [1] 2 1
>> nrow(B)
> [1] 2
>
>
>
> tutti i telefonini TIM!
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT

Hello

I wonder whether I can find rmutil (it seem to be part of rcode or something
like that)?

Many thanks

Ed